I know someone making a PS4 only game that is absolutely cutting edge for a huge AAA studio, and she says that it's just shy of being unsustainable in terms of development cost and effort. She said that she really thinks this is the wall, and the generation after this is going to be impossible to sustain unless something is done.

So it'll happen out of necessity. Developers are going to realize that a secret door adds more to the world than huge set pieces and cutscenes. That scaling back and creating a smaller more intimate world with more to do (and more you can miss), makes the world feel bigger and players engage more.

The levels in Human Revolution are larger and more detailed than in Deus Ex, so why is hong kong in Deus Ex more immersive than Shanghai in HR? Because HR forgot that Deus Ex was great because everything was below the surface. HR actively pushes sidequests and secrets on you instead of hiding them and not telling you. You are rewarded for gaming the aug system to explore in Deus Ex by finding cool shit, some of which significantly changes the way you view the game. In HR, you are steered that way so you can feel good for finding secrets!

It may take one more generation, but we will go back to Deus Ex's way of doing things, and resources will be spent hiding more rather than showing more.